1. Field of the Invention
The present invention relates generally to an electric motor for use in a machine. More specifically, the present invention concerns an electric motor that includes a rotor, an insulated stator, and a mounting cap.
2. Discussion of the Prior Art
Those of ordinary skill in the art will appreciate that electric motors are often used in home appliances such as dishwashers and washing machines. In a washing machine, for instance, an electric motor may be used to cause rotation of the washer basket to agitate the clothing contained therein. Although a variety of motor component arrangements may be used, one known embodiment of an electric motor includes a stator positioned at least in part radially inside a rotor. An electric motor having such a configuration is commonly referred to as an outer rotor motor or external rotor motor, although other names may be used. In the case of a washing machine having an electric motor of this sort, the rotor is typically coupled to the washer basket, whereas the stator is fixed to a tub mounting hub that is coupled to a stationary washer outer tub. To avoid potential electrical shock of the user, the stator is mounted in such a manner that it is electrically isolated from the tub.
The stator of an outer rotor motor typically includes a core and a plurality of coils. Conventionally, the core takes a generally toroidal form and is composed of a ferromagnetic metal such as iron or steel. The core typically includes a plurality of teeth projecting radially outwardly and defining slots therebetween. The coils are formed by the winding of electrically conductive wire multiple times around each tooth to at least partially fill the slots. Copper wire is commonly used due to its low electrical resistivity.
The rotor of an outer rotor motor typically includes a shaft, a support structure coupled to the shaft, and a plurality of permanent magnets supported by the support structure so that they circumscribe the stator in a spaced relationship. When an electrical current flows through the coils formed around each tooth of the stator core, the ferromagnetic material of the core is energized to form a plurality of magnetic fields corresponding to the teeth. These stator magnetic fields interact with the magnetic fields produced by the permanent magnets of the rotor to induce relative rotation between the rotor and stator. The direction of each magnetic field is dependent on the direction of the current flow around the respective tooth. Although a variety of approaches may be used to ensure appropriate field directions, one embodiment of an electric motor includes a stator having coils wound clockwise around some teeth and coils wound counter-clockwise around other teeth to produce oppositely directed magnetic fields within the same stator when the wires are exposed to a direct current.
While conventional outer rotor motors have been satisfactory in some respects, those of ordinary skill in the art will appreciate that conventional motors often have large cores. The metal of these cores is both expensive and heavy, leading to higher costs and decreased efficiency. Furthermore, use of the metal core to mount the stator in the machine is often inconvenient and expensive. More particularly, traditional outer rotor motors are also limited to a specific mounting arrangement incorporated into the core fabrication process. To use a conventional core in a different application requiring a different mounting arrangement, the core fabrication process must be varied (e.g., the lamination die for a laminated stator core must be re-machined).
Traditional stator designs also often use expensive copper wire and complicated and unwieldy insulation arrangements that virtually prevent the use of alternative, less expensive wiring, especially in confined applications having certain power requirements. Even with aluminum wound stators (such as a powder coated stator core wound with aluminum wiring), mounting of the stator, particularly within different machine applications, is still often a problem. Yet further, traditional designs often fail to assuredly secure wiring in place on the core.